Liquid level differential sensing device



March 9, 1965 c. H. NORDELL 3,172,347

LIQUID LEVEL DIFFERENTIAL SENSING DEVICE Filed Sept. '7, 1962 2Sheets-Sheet l q .T L

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March 9, 1965 c, NORDELL 3,172,847

LIQUID LEVEL DIFFERENTIAL SENSING DEVICE Filed Sept. '7, 1962 2Sheets-Sheet 2 United States Patent 3,172,347 LKQTJID LEVEL DIFFERENTHALSENSRNG DEVTCE Carl E. Nordeil, Crystal Bay, Nev. Filed Sept. 7, 1962,Ser. No. 222,617 4 Claims. (Cl. 21il1tl7) The invention relates to aliquid level differential sensing device, and is particularly concernedwith a control switch operable in response to the liquid leveldifferential across the screen of a comminuting device positioned in aflowing stream of sewage or other liquid containing solids to becomminuted, to start and stop operation of the comminuting device.

The present invention provides means for starting and stopping the motorof a comminuting device of the type referred to, so that it will operateonly when the operation is warranted by an accumulation of solids on theupstream surface of the screen.

In general, comminuting devices of the type referred to comprise ascreen, a cutting cylinder rotatably mounted in association with thescreen, a motor for rotating the cutting cylinder, and means for movingthe cutting cylinder across the upstream surface of the screen. Thescreen and comminuting device are positioned in a stream of sewage orother liquid and the screen serves to intercept solids from the liquidstream flowing through the screen, and the cutting cylinder cooperateswith the screen and/ or with a comb adjacent the cutting cylinder tocomminute the intercepted solids so that they can flow through thescreen along with the liquid.

Installations having a heavy flow of sewage require constant operationof the comminuting device, but in many cases the flow of sewage isirregular and there are periods of very low flow when operation of thecomminuting device is not required. The present invention is ofparticular advantage in connection with installations where thecontinuous operation of the comminuting device is not necessary. Theinvention provides control means to actuate a switch for starting themotor of the comminuting device when the solids intercepted by thescreen block the flow of liquid through the screen to such an extentthat the liquid level on the upstream side of the screen is raised apredetermined distance above the liquid level on the downstream side ofthe screen. As said solids are comminuted, the flow of liquid throughthe screen increases until the difference in liquid levels on oppositesides of the screen substantially disappears. When the liquid levelbecomes the same on both sides of the screen, the control means opensthe switch to stop the motor of the comminuting device.

The control means of the present invention consists essentially of adiaphragm controlled switch that is actuated in response to a pressuredifferential that is caused by differences in the liquid level on theupstream and downstream sides of the screen of the comminuting device.The switch is opened to stop the motor of the comminuting device whenthe liquid level is approximately the same on both sides of the screen.Stopping the motor of the comminuting device whenever its operation isnot required extends the useful life of the motor and the comminutingdevice. The control operates continuously to start the motor wheneveroperation of the comminuting device is required and to stop it wheneveroperation of the comminuting device is not required.

The structure by means of which the above noted and other advantages ofthe invention are attained will be described in the followingspecification, taken in conjunction with the accompanying drawings,showing a preferred illustrative embodiment of the invention, in which:

FIGURE 1 is a front elevational view of the pressure responsive controlunit, with the cover of its cabinet removed;

FIG. 2 is a vertical sectional view of the control unit, taken on line2-2 of FIG. 1, showing parts in elevation, and illustratingschematically a comminuting device and the conduits on opposite sides ofthe screen which form a part of the control unit;

FIG. 3 is a cross sectional view of the diaphragm switch controlassembly shown in FIG. 1;

FIG. 4 is a cross sectional view taken on line 4-4 of FIG. 3;

FIG. 5 is a fragmentary detail sectional view taken along the line 55 ofFIG. 3; and

FIG. 6 is a fragmentary detail sectional view similar to FIG. 5, showingthe switch in open position.

Referring to FIG. 2 of the drawings, the control unit is mounted in acabinet, generally indicated at 10, and is connected, in a mannerhereinafter described, to a pair of rigid conduit sections 11, 12. Therigid conduit sec tions are arranged one on each side of the screen of acomminuting device 13 that is driven by a motor 14. The screen (notshown) is mounted in the frame 15 of the comminuting device 13. Asshown, conduit section 11 is located on the upstream side of the screen,and conduit section 12 is located on the downstream side. These conduitsections are mounted securely in vertical position and each has an openbottom 16 and 17, respectively, equally spaced from the bottom 18 of thetrough through which the sewage 19 or other liquid flows. The mountingis such that said open lower ends of the conduits are always submergedat the same level in the sewage 19 or other liquid being treated. Eachrigid conduit section 11, 12, is connected at its upper end to thecontrol unit by means of a flexible conduit section 20, 21,respectively.

Referring to the specific form of control unit illustrated, said unitincludes a pair of conventional atmospheric pumps 22, 23, and adiaphragm-switch housing 24. A bracket 25 holds both pumps in cabinet10. The housing 24, shown in FIG. 3, preferably comprises two externallyflanged housing sections 26, 27, that are held together by screws 28(FIG. 1). Housing 24 has a flexible diaphragm 29 secured betweensections 26, 27. The diaphragm divides the housing into two chambers 30,31, hereinafter referred to as the downstream chamber and the upstreamchamber, respectively. The diaphragm carries suitable washers 32 heldagainst its opposite surfaces by a screw 33 which also serves to secureone leg 34 of a U-shaped bracket 35 against one washer for movement withthe diaphragm. Bracket 35 extends into the downstream chamber andloosely embraces a normally open micro switch 36 supported on a bracket37 mounted on the inside face of the related housing section 27. Thisswitch is connected through a lead 38 to the electric circuit forstarting and stopping operation of the motor 14 that drives thecomminuting device.

A tapped opening 39 communicating with upstream chamber 31 is connectedby the flexible conduit section 20 to the upper end of the rigid conduitsection 11, and a tapped opening it communicating with downstreamchamber 39 is connected by the flexible conduit section 21 to the upperend of the rigid conduit section 12. Re ferring specifically to FIG, 1,the downstream conduit section 21 has a T-fitting 41 therein to which isconnected a conduit section 42 leading from the compression side ofatmospheric pump 22, the latter being provided with a pressureregulating knob 43. A similar T- fitting 44 and conduit section 45connects conduit section 20 with the other atmospheric pump 23, havingpressure regulator knob 46 thereon. The pressure regulator knobs 43 and46 may be adjusted to cause the switch 36 to be operated automaticallyat any desired pressure differential on opposite sides of the screen.

The atmospheric pumps 22, 23 are operated so as to maintain suflicientpressure in the conduits to cause air bubbles to escape continuouslyfrom the open bottom end of each conduit section 11 and 12. Eachatmospheric pump is enclosed in a chamber having no outlet .except thelowermost end of the conduit 42 or 45 communicating therewith, and thelower end of each conduit section 11, 12 is closed by a column of sewageor other liquid in which they are immersed. The pressure exerted by eachpump to force air bubbles through its conduit depends upon the height ofthe liquid column in the lower end of said conduit. This pressure isexerted equally in all directions and tends to force the flexiblediaphragm, which constitutes a portion of the wall of each chamberoutwardly. When the height of the liquid column in the lower section ofeach conduit is the same, the pressure exerted by each pump is equal,and

the diaphragm retains its normal position.

As solids intercepted by the screen accumulate on the upstream surfaceof the screen, the level of liquid 19 on the upstream side of the screenrises. This increase .in the liquid level increases the height of thecolumn of liquid in conduit section ill, and the pump connected toconduit section 11 is required to exert increased pressure to force theair bubbles through said conduit section. Since this increased pressureis greater than the pressure exerted against the opposite surface offlexible diaphragm 29, it moves the diaphragm toward switch 36. When,the pressure differential is sufficient, screw 33, carried by thediaphragm, depresses plunger 47 to close the switch and thereby startoperation of the comminuting device.

During the operation of the comminuting device, solids accumulated onthe upstream side of the screen are comminuted, and, as the accumulatedsolids are comminuted, the flow capacity of the screen is restored tonormal. As

the flow capacity of the screen is increased, the difference between theliquid levels on opposite sides of the screen gradually diminishes. Thisultimately results in diminished pressure in the upstream chamber 31 ofthe switch housing. When the pressure in chamber 31 has diminishedsufficiently, the diaphragm 29 returns to its normal position. Theupward movement of diaphragm 29, as viewed in FIG. 3, carries bracket 35upwardly so as to move the leg 49 of bracket 35 into engagement with areset button 48. The upward movement of reset button .48 shuts off motor14 and thereby stops operation of the comminuting device. The electricalcircuit is so arranged that operation of the comminuting device isstopped only when the cutting cylinder of the comminuting device is atthe top of its travel.

The actuation of the switch 36 by the pressure caused by the differencein the liquid level on opposite sides of the screen insures operation ofthe comminuting device when the accumulation of solids on the upstreamside of the screen is suflicient to require comminution, and preventsoperation of the comminuting device when the acto variations in theliquid level of different portions of a body of liquid, said devicecomprising a diaphragm, a

switch means mounted on said diaphragm for operating said switch inopposite directions, and two air pumps voperable to move said diaphragm,said air pumps being connected to air escape conduits each of which hasan open lower end immersed in liquid and a column of liq uid in thelower end portion of each of said conduits, the lower ends of saidconduits being spaced equally from the bottom of said liquid, each ofsaid air pumps being operated continuously to force a stream of airbubbles through the liquid in the lower end of the air escape conduitconnected thereto, the greater height of the column of liquid in the airescape conduit immersed in the portion of said liquid having a higherliquid level causing the air pump connected thereto to increase the airpressure exerted by it to force air bubbles therethrough and therebymove said diaphragm in one direction against the pressure exerted bysaid other air pump, movement of said diaphragm a predetermined distancein either direction carrying said means into operative engagement withsaid switch.

2. A liquid level differential sensing device comprising a housing, adiaphragm dividing said housing into two separate chambers, a U-shapedbracket having two parallel legs, one of said legs being securedadjacent said diaphragm, said bracket being movable with said diaphragm,

a conduit in how communication with one chamber and opening into a bodyof liquid, at second conduit in flow communication with the otherchamber and opening into a different portion of said liquid, meansoperable to maintain sufiicient air pressure in each of said conduits toforce a stream of air bubbles therethrough, said means being efifective,when the level of one portion of said liquid reaches a predetermineddifferential relative to the level of the other portion of said liquid,to cause a sufficient diiferential in the air pressure in said chambersto displace the diaphragm, a switch mounted in one of said chambersbetween the parallel legs of said bracket, a depressible plungerprojecting from one side of said switch and engageable by one of saidlegs, and a depressible reset button projecting from the opposite sideof said switch, said plunger being operable by said diaphragm, when saiddiaphragm is moved in one direction, to close said switch, and saidreset button being operable by said second leg of said bracket, whensaid diaphragm is moved in the op posite direction, to open said switch.

3. A liquid level diflferential sensing device comprising a housing, aswitch enclosed in said housing, a diaphragm in said housing dividingthe housing into two chambers, two switch actuating members projectingfrom one side of said diaphragm, two atmospheric pumps one beingconnected with each chamber, and conduits connecting each of said pumpswith different portions of a body of liquid, each of said conduitshaving an open end immersed in one of said portions or" liquid andforming a passage through which air forced from either of said chambersby its pump escapes into said liquid, said open ends of the conduitsbeing disposed at the same level, thereby causing the pump connected tothe portion of the body of liquid having the higher liquid level toincrease the pressure in the chamber connected thereto, said pressureincrease displacing said diaphragm, movement of said diaphragm to apredetermined distance in one direction carrying one of said switchactuating members into switch closing position, and movement of saiddiaphragm to a predetermined distance in the opposite direction carryingsaid other switch actuating member into switch opening position.

4. In combination with a comminuting device comprising a screen immersedin a stream of sewage for intercepting solids from said sewage, acutting cylinder ro tatably mounted for cooperation with said screen,and a motor for moving said cutting cylinder across the surface of saidscreen; a liquid level sensing device responsive to variations in theliquid level of said sewage on opposite sides of said screen, saidsensing device comprising a diaphragm, a switch operable to energizesaid motor in closed position and to deenergize it in open position,means mounted on said diaphragm for opening and closing said switch, andair pressure means operable to move said diaphragm, movement of saiddiaphragm a predetermined distance in one direction moving said firstmentioned means to switch opening position and movement of saiddiaphragm a predetermined distance in the opposite direction moving saidfirst mentioned means to switch closing position, said air pressuremeans including air escape conduits opening into said sewage on oppositesides of said screen.

References Cited in the file of this patent UNITED STATES PATENTSKnowles Nov. 28, 1933 Kuster Sept. 7, 1937 Levy May 8, 1956 Byrkett May14, 1957 Davis Feb. 25, 1958 Lannert Dec. 1, 1959

1. A LIGUID LEVEL SENSING DEVICE OF A TYPE RESPONSIVE TO VARIATIONS INTHE LIQUID LEVEL OF DIFFERENT PORTIONS OF A BODY OF LIQUID, SAID DEVICECOMPRISING A DIAPHRAGM, A SWITCH MEANS MOUNTED ON SAID DIAPHRAGM FOROPERATING SAID SWITCH IN OPPOSITE DIRECTIONS, AND TWO AIR PUMPS OPERABLETO MOVE SAID DIAPHRAGM, SAID AIR PUMPS BEING CONNECTECD TO AIR ESCAPECONDUITS EACH OF WHICH HAS AN OPEN LOWER END IMMERSED IN LIQUID AND ACOLUMN OF LIQUID IN THE LOWER END PORTION OF EACH OF SAID CONDUITS, THELOWER ENDS OF SAID CONDUITS BEING SPACED EQUALLY FROM THE BOTTOM OF SAIDLIQUID, EACH OF SAID AIR PUMPS BEING OPERATED CONTINUOUSLY TO FORCE ASTREAM OF AIR BUBBLES THROUGH THE LIQUID IN THE LOWER END OF THE AIRESCAPE CONDUIT CONNECTED THERETO, THE GREATER HEIGHT OF THE COLUMN OFLIQUID IN THE AIR ESCAPE CONDUIT IMMERSED IN THE PORTION OF SAID LIQUIDHAVING A HIGHER LIQUID LEVEL CAUSING THE AIR PUMP CONNECTED THERETO TOINCREASE THE AIR PRESSURE EXERTED BY IT TO FORCE AIR BUBBLESTHERETHROUGH AND THEREBY MOVE AND DIAPHRAGM IN ONE DIRECTION AGAINST THEPRESSURE EXERTED BY SAID OTHER AIR PUMP, MOVEMENT OF SAID DIAPHRAGM APREDETERMINED DISTANCE IN EITHER DIRECTION CARRYING SAID MEANS INTOOPERATIVE ENGAGEMENT WITH SAID SWITCH.
 4. IN COMBINATION WITH ACOMMUNUTING FEVICE COMPRISING A SCREEN IMMERSED IN A STREAM OF SEWAGEFOR INTERCEPTING SOLIDS FROM SAIDS SEWAGE, A CUTTING CYLINDER ROTATABLYMOUNTED FOR COOPERATION WITH SAID SCREEN, AND A MOTOR FOR MOVING SAIDCUTTING CYLINDER ACROSS THE SURFACE OF SAID SCREEN; A LIQUID LEVELSENSING DEVICE RESPONSIVE TO VARIATIONS IN THE LIQUID LEVEL OF SAIDSEWAGE ON OPPOSITE SIDES OF SAID SCREEN, SAID SENSING DEVICE COMPRISINGA DIAPHRAGM, A SWITCH OPERABLE TO ENERGIZE AND MOTOR IN CLOSED POSITIONAN TO DEENERGIZE IT IN OPEN POSITION, MEANS MOUNTED ON SAID DIAPHRAGMFOR OPENING AND CLOSING SAID SWITCH, AND AIR PRESSURE MEANS OPERABLE TOMOVE SAID DIAPHRAGM, MOVEMENT OF SAID DIAPHRAGM A PREDETERMINED DISTANCEIN ONE DIRECTION MOVING SAID FIRST MENTIONED MEANS TO SWITCH OPENINGPOSITION AND MOVEMENT OF SAID DIAPHRAGM A PREDETERMINED DISTANCE IN THEOPPOSITE DIRECTION MOVING SAID FIRST MENTIONED MEANS TO SWITCH CLOSINGPOSITION, SAID AIR PRESSURE MEANS INCLUDING AIR ESCAPE CONDUITS OPENINGINTO SAID SEWAGE ON OPPOSITE SIDES OF SAID SCREEN.